Digital Vestigial Sideband (VSB) is the modulation format selected as the US terrestrial broadcast standard. As with all digital modulation formats, a critical aspect of receiver design is the handling of multipath, especially severe multipath interference combined with a marginal signal-to-noise ratio. The severity of the problem is maximized with indoor antennas used in urban environments. This is because, in urban environments, there are numerous buildings which tend to interfere with reception while also reflecting the transmitted signal leading to significant multipath interference. At present, multipath is handled by an equalizer in the demodulator portion of a receiver.
Despite recent improvements in equalizer design, signal reception under strong multipath conditions remains a technical problem confronting digital terrestrial broadcast.
In the context of satellite and analog television systems, various attempts have been made to improve reception by controlling one or more antenna characteristics. Unfortunately, such attempts have, for the most part, focused on satellite antennas or have generally ignored issues relating to multipath interference. Furthermore, such system generally ignore and/or issues relating to the receiver/antenna interface.
For example, U.S. Pat. No. 6,111,542 describes a user terminal including a rotating electronically steerable antenna system which combines coarse mechanical beam steering with fine electronic beam steering to provide full hemispherical coverage and enable hand-offs in a satellite communication system. Unfortunately, this reference fails to address issues relating to multi-path interference or to provide a simple control mechanism by which a digital receiver can automatically control multiple antenna characteristics.
The abstract of Published Japanese Patent Application 61296573 describes an adaptive antenna system which generates a steering signal based on an MSN algorithm implemented by a processor coupled to the antenna. The generated steering signal is used to adjust a directivity characteristic of an antenna element so that the major beam will be directed to the desired wave incoming direction even if the incoming direction of the desired wave is changed. As with the preceding reference, this reference fails to address issues relating to multi-path interference or to provide a simple control mechanism by which a digital receiver can automatically control multiple antenna characteristics.
U.S. Pat. No. 5,771,015 describes a system which relies on viewer input to select from a plurality of possible antenna settings. The described system includes a controllable antenna intended for indoor use as part of a television system. The system includes various electromechanical assemblies for controlling physical attributes of the antenna such as the orientation of antenna elements about a vertical axis, the length of antenna elements, the angular orientation of a loop antenna about a vertical axis, etc. Electrical attributes of the antenna such as the gain of variable gain elements can also be controlled. A viewer of the system selects what is perceived to be the optimum settings for a particular channel and the settings are stored for future use when the channel is selected. The described system has the disadvantage of relying on viewer input to determine the appropriate antenna settings. The need for such input results in a relatively complicated and non-user friendly control system. Furthermore, the specific problem of multipath interference is not addressed by the reference.
Given the challenges presented by multipath interference, there remains a need for antenna designs which are intended to eliminate and/or reduce the effect of multipath on received signals. In addition, while various systems have addressed controlling various physical and electrical characteristics of an antenna, there remains room for improvement in the way antennas are controlled. In particular, there is a need for improved antenna control methods which eliminate the need for viewer input. There is also a need for improvements in the number of antenna characteristics that can be controlled, and for improvements in the signaling techniques used to control antenna settings. Furthermore, in order to provide increased reliability and reduce manufacturing costs, it is desirable that the use of movable mechanical parts be reduced and/or eliminated at least in some embodiments.